Martin Klingensmith nnytech.net> writes: > That is correct (your calculations) I am not at all sure of that. With 12kW sun and 2hp compressor in and 5hp out efficiency is about 20% without the compressor, 15% with, as you said (and not as I said). But there is no way to tell what energy the air tank stored so input from the compressor could be rated twice as high (easily). There are too many assumptions being made to be able to draw any conclusions imho. When working with steam there is a simple way to find out things: efficiency betrays the working pressure and thus the minimum steam temperature. Since the efficiency cannot exceed Carnot efficiency figures like 15% efficiency mean Thot = 1/0.85 * 400K (400K since the exhaust is steam at 1bar, hence Tc >= 100 deg C ~= 400K). That's about 470K for Th and corresponds to 8bar water steam pressure. This is towards the low end of what is probably being used. Aditionally water becomes very equipment-unfriendly above about 250 degrees C (40+bar and temperature plus water begins to be very reactive if it has any dissolved O2). With 250 deg. C Th and 30 deg. C. Tc (condensing) Carnot = 40% (and this is not achieved even by the best Stirling motors). The only thing I am fairly confident is true is, that the motor is nothing very revolutionary efficiency-wise. I once wrote on this list that someone should try to run a standard air tool (disk grinder f.ex.) using steam to see what happens. It is likely that any non-plastic grinder will survive the experience quite well (manganese and aluminium constructions even more so and the palettes in the rotor are usually phenolic). That would be a $40 1-2hp steam engine (with the first reduction gear built in for free, together with a sturdy shaft). While a normal air motor will not like 165 deg. C steam (corresponds to 6bar which is the working pressure of many air tools), with some modifications (like new ptfe gaskets and plastic parts and so on) it could be made to work imho. The pressure range for steam in 'Victorian' style boylers is in range for most air tools (under 10bar, under 200 deg C) and most 'homemade' technology. Playing with homemade steam pressure is extremely dangerous. Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist